Petti: On pitcher aging curves

From SABR member Bill Petti at FanGraphs on April 30, 2012:

As on-field performance data has evolved, baseball enthusiasts have been spoiled with more precise measures of player performance. One area in particular is pitcher velocity. Whether through Baseball Info Solutions (BIS) or Pitch FX, writers and researchers can now add a critical variable into their analysis that wasn’t readily available a decade ago.

Many readers of FanGraphs and Beyond the Box Score have seen Jeff Zimmerman‘s position player aging curves. After reviewing them, I started to pester Jeff to see if he considered similar curves for pitchers — specifically in the area of fastball velocity. I was curious about the general pattern of decline for fastball speed and how it impacts overall pitcher performance. Luckily, Jeff already had been thinking about this.

Today, Jeff and I are launching a multi-part series on pitcher aging curves, which is centered on fastball velocity. This introductory article will lay out the methodology we used and — of course — the initial baseline curves for all pitchers, as well as starters versus relievers.